1. Field of the Invention
The present invention relates to an antenna with multiple resonating conditions, and more particularly, to an antenna generating multiple resonating conditions with one or more radiating-condition generating elements connected to ground, to achieve broadband operations.
2. Description of the Prior Art
An antenna is used for transmitting or receiving radio waves, to communicate or exchange wireless signals. An electronic product with a wireless communication function, such as a laptop, a personal digital assistant (PDA), usually accesses a wireless network through a built-in antenna. Therefore, for facilitating the user to access the wireless communication network more easily, an ideal antenna should have a wide bandwidth and a small size to meet the trends of compact electronic products within a permitting range, so as to integrate the antenna into a portable wireless communication equipment.
In the prior art, one of the common antennas for wireless communication is a planar inverted F antenna (PIFA), as implied by the name, whose shape is similar to a rotated and inverted “F”. Please refer to FIG. 1A and FIG. 1B, FIG. 1A is a schematic diagram of a conventional PIFA antenna 10, and FIG. 1B is a schematic diagram of voltage standing wave ratio (VSWR) of the PIFA antenna 10. As shown in FIG. 1A, the PIFA antenna 10 includes a grounding element 100, a radiating element 102, a connection element 104 and a feed-in element 106. The connection element 104 connects the grounding element 100 and the radiating element 102, such that a resonating path of a monopole antenna is reduced from a half wavelength to a quarter wavelength, and thus the size of the antenna can be reduced effectively.
Besides, as can be seen from FIG. 1B, the PIFA antenna 10 only has one resonating condition. However, as the wireless communication technology progresses, operating frequencies of different wireless communication systems may be different; therefore, an ideal antenna should cover bandwidths of different wireless communication networks within a single antenna. In such a situation, the prior art further derives a dual-band antenna with two resonating conditions from the PIFA antenna 10.
Please refer to FIG. 2A and FIG. 2B. FIG. 2A is a schematic diagram of a conventional dual-band antenna 20, and FIG. 2B is a schematic diagram of VSWR of the dual-band antenna 20. The dual-band antenna 20 includes a grounding element 200, a radiating element 202, a connection element 204 and a feed-in element 206. The radiating element 202 is composed of a first radiator 2020 and a second radiator 2022 corresponding to high frequency band and low frequency band, respectively. The connection element 204 is composed of branches 2040 and 2042 connected together. The branch 2040 is connected to the radiating element 202 and the feed-in element 206, and the branch 2042 is connected to the feed-in element 206 and the grounding element 202. As can be seen from FIG. 2A, the dual-band antenna 20 has advantages of low profile, i.e. a small height, small size and easy production. Meanwhile, as can be seen from FIG. 2B, the dual-band antenna 20 has dual resonating conditions suitable for dual-band application, and achieves the optimization of the antenna characteristic.
Although the dual-band antenna 20 can achieve dual resonating conditions, for a wireless communication system with broad bandwidth, such as long term evolution (LTE) system, the bandwidth of the dual-band antenna 20 is still not enough, resulting in limitations of its application range. Therefore, how to increase bandwidth of an antenna has become one of the goals in the wireless technology industry.